The government's plan to set up a centralised efficiency body to power its public savings programme has been hit by delays, official government documents reveal.

The efficiency and reform group (ERG), charged with making the whole of government leaner by establishing joint procurement programmes and vetting the biggest new contracts, is central to the coalition's plans to drive down costs across Whitehall.

Ian Watmore, the former chief executive of the FA, was appointed to head it in June.

But ministerial documents reveal that it was granted its full powers on 20 December, lagging behind a November deadline in the Cabinet Office's business plan –a document introduced by the government to monitor progress on the coalition's reforms.

The document cites the November deadline to "establish the efficiency and reform group as the central authority for the government's major projects". Up until last week it was officially overdue, with the January update confirming that it was signed off just before Christmas.

Tonight, the Cabinet Office rushed to amend the Number 10 website, where a prominent version of the business plan was still marked overdue and appeared not to have been updated since the beginning of December.

It is the second embarrassing assessment of the Cabinet Office's work to emerge in the past week after the public administration select committee was accused of "botching" its review of quangos, failing properly to decide which agencies were closed, saved or reformed in its so-called "bonfire of the quangos".

Oliver Letwin, the cabinet office minister, will face questions from the public administration select committee on progress on business plans.

The committee was also profoundly critical of the cabinet office's business plan in last week's quango report. The report accused the government of undermining the scheme, after it identified inaccuracies in the cabinet office's plan.

"We welcome the intention behind the publication of departmental business plans, but they will only be useful tools to help the public hold the government to account if the information contained in them is accurate," it warned.

A spokesman for the cabinet office said that the ERG had been signed off as the "central authority" for signing off major projects above £50m in cost on December 20 and was now fully up and running.